The present invention relates to a process for producing C1-C10 aldehydes by oxidative dehydrogenation of C1-C10 alcohols over a shaped catalytst body which comprises shaped silver-containing fibers and/or threads, wherein the average diameter of these silver-containing fibers and/or threads is in the range from 30 μm to 200 μm.
The process for producing formaldehyde by oxidation/dehydrogenation of methanol over a silver catalyst is long known, see for example Ullmann's Encyclopedia of Industrial Chemistry, 2005, pages. 1 ff.
The silver catalyst used can be used in various forms. For example as granular crystalline silver but also in the form of silver nets or silver gauze.
U.S. Pat. No. 4,076,754 (Du Pont) describes a two-stage process for the manufacture of formaldehyde from methanol, air and water. The catalyst used comprises 40 superposed sheets of 20 mesh silver gauze (i.e., mesh size 1.25 mm) made from silver wire 0.014 inch (i.e., 350 μm or 0.35 mm) in diameter. The density or the void fraction of the silver gauze is not disclosed in U.S. Pat. No. 4,076,754.
DE 2829035 A1 (Heraeus) describes a catalyst comprising catalytically active metallic fibers which consist of silver, platinum, rhodium, palladium or an alloy based on one thereof, wherein the metallic fibers are interconnected feltlike in the manner of a needle-bonded composite. The catalyst can be used for ammonia oxidation and the manufacture of hydrocyanic acid or formaldehyde. The cross section of a ribbon-shaped fiber can be rectangular with the dimensions of 100 μm and 50 μm, the length can be between 10 cm and 1 m. The density or the void fraction of the interfelted metallic fiber body is not described.
DE 3047193 A1 (Johnson Matthey) describes a catalyst made of silver or a silver alloy. The catalyst body is produced by melt spun process or melt extraction process. For example, a ribbon 1 to 2 mm in width and 50 to 60 μm in thickness is processed by crimping and cutting to yield undulating catalyst bodies about 1 cm in length and hence rather short-fibered. DE 3047193 A1 does not disclose a braid, knit, felt or the like formed from these catalyst bodies.
Although the catalytic oxidation/dehydrogenation of alcohols to aldehydes, more particularly methanol to formaldehyde, is already long known, there is still room for improvement, for example an increase in catalytic activity, in formaldehyde selectivity, advantageously for unchanged catalytic activity, or in the pressure drop over the catalyst.
Applicant studies have shown, particularly with regard to the oxidative dehydrogenation of methanol to formaldehyde, that it is not a straightforward matter to use fiber- or wire-containing structures as catalysts. This is because the constitution of the shaped catalyst body has to make it possible to establish a stable ignited reaction zone under the operating conditions of the industrial process for example of the oxidative dehydrogenation of methanol to formaldehyde. However, the current state of the art does not disclose the requisite features of such a shaped catalyst body.